This invention relates to synthetic dichroic plane polarizers based on molecularly oriented polyvinyl alcohol sheets and, in particular, to a high efficiency K-type polarizing sheet.
Normally, light waves vibrate in a large number of planes about the axis of a light beam. If the waves vibrate in one plane only, the light is said to be plane polarized. Several useful optical ends and effects can be accomplished by plane polarized light. For example, in the manufacture of electrooptical devices, such as liquid crystal display screens, crossed polarizers are used in conjunction with an addressable liquid crystal interlayer to provide the basis for image formation. In the field of photography, polarizing filters have been used to reduce the glare and the brightness of specular reflection. Polarizing filters (circular or otherwise) have also been used for glare reduction in display device screens.
Linear light polarizing films, in general, owe their properties of selectively passing radiation vibrating along a given electromagnetic radiation vector (and absorbing electromagnetic radiation vibrating along a second given electromagnetic radiation vector) to the anisotropic character of the transmitting film medium. Dichroic polarizers are absorptive, linear polarizers having a vectoral anisotropy in the absorption of incident light. The term xe2x80x9cdichroismxe2x80x9d is used herein as meaning the property of differential absorption (and transmission) of the components of an incident beam of light depending on the direction of vibration of the components. Generally, a dichroic polarizer will transmit radiant energy along one electromagnetic vector and absorb energy along a perpendicular electromagnetic vector. A beam of incident light, on entering a dichroic polarizer, encounters two different absorption coefficients, one low and one high so that the emergent light vibrates substantially in the direction of low absorption (high transmission).
Among synthetic dichroic polarizers are K-type polarizers. A K-type polarizer derives its dichroism from the light-absorbing properties of its matrix, not from the light-absorbing properties of dye additives, stains, or suspended crystalline material. Typically K-type polarizers comprise a sheet of oriented poly(vinyl alcohol) having an oriented suspension of a dehydration product of polyvinyl alcohol (i.e., polyvinylene). K-type polarizers of this kind are formed by heating the polymeric sheet in the presence of a dehydration catalyst, such as vapors of aqueous hydrochloric acid, to produce conjugated polyvinylene blocks and unidirectionally stretching the polymeric sheet prior to, subsequent to, or during the dehydration step to align the poly(vinyl alcohol) matrix. By orienting the poly(vinyl alcohol) matrix unidirectionally, the transition moments of the conjugated polyvinylene blocks or chromophores are also oriented and the material becomes visibly dichroic. A second orientation step or extension step may be employed after the dehydration step as described in U.S. Pat. No. 5,666,223 (Bennett et al.). Summary of the Invention
In general, in one aspect, the invention features a method for making a polarizer from a polymeric sheet having a predetermined original length and including a hydroxylated linear high polymer. The polymeric sheet is stretched from greater than 5.0 times to approximately 6.0 times the original length. A suitable dehydration catalyst is introduced to the polymeric sheet. The polymeric sheet and the catalyst is heated at a temperature appropriate to effect partial dehydration of the polymeric sheet wherein light absorbing, vinylene block segments are formed.
Implementations of the invention may also include one or more of the following features. The hydroxylated linear high polymer may be polyvinyl alcohol, polyvinyl acetal, polyvinyl ketal, or polyvinyl ester. The introducing step may include exposing the polymeric sheet to fuming acidic vapors. The introducing step may include coating the polymeric sheet with an acid coating. The introducing step may include placing an acid donor layer adjacent to the polymeric sheet and exposing the acid donor layer to a radiant energy to release one or more molecules of acid. The radiant energy may be thermal energy or ultraviolet light energy. The stretching may be bidirectional relaxed, bidirectional unrelaxed, unidirectional relaxed, unidirectional unrelaxed, or parabolic.
The method may include subjecting the polymeric sheet to a boration treatment at an elevated temperature. The method may also include unidirectionally extending the stretched and heated polymeric sheet greater than 0% to about 70% of the stretched length. The subjecting step and the extending step may be performed concurrently. The subjecting step may be performed before the extending step. The boration treatment temperature may be greater than about 80xc2x0 C.
The method may include adding at least one dichroic dye to the polymeric sheet. The method may include subjecting the polymeric sheet to a boration treatment at an elevated temperature, wherein the adding step and the subjecting step are performed concurrently. The method may include subjecting the polymeric sheet to a boration treatment at an elevated temperature, wherein the adding step is performed before the subjecting step. The dichroic dye may be a yellow dye, a blue dye, or a combination thereof. The boration treatment may include placing the polymeric sheet in contact with an aqueous solution comprising boric acid. The boric acid concentration may range from about 5% to about 20%. The aqueous solution may include borax. The borax concentration may range from about 1% to about 7%. The at least one dichroic dye may be a yellow dye, a blue dye, or a combination thereof. The polymeric sheet may be supported on a carrier web or a support layer.
In general, in another aspect, the invention features a method for making a polarizer from a polymeric sheet having a predetermined original length and including a hydroxylated linear high polymer. The polymeric sheet is stretched from approximately 3.5 to approximately 6.0 times the original length. A suitable dehydration catalyst is introduced to the polymeric sheet. The polymeric sheet and the catalyst is heated at a temperature appropriate to effect partial dehydration of the polymeric sheet wherein light absorbing, vinylene block segments are formed. The polymeric sheet is subjected to a boration treatment at a temperature greater than about 80xc2x0 C. The polymeric sheet is unidirectionally extended greater than 0% to about 70% of the stretched length.
Implementation of the invention may also include one or more of the following features. The hydroxylated linear high polymer may be polyvinyl alcohol, polyvinyl acetal, polyvinyl ketal, or polyvinyl ester. The introducing step may include exposing the polymeric sheet to fuming acidic vapors. The introducing step may include coating the polymeric sheet with an acid coating. The introducing step may include placing an acid donor layer adjacent to the polymeric sheet and exposing the acid donor layer to a radiant energy to release one or more molecules of acid. The radiant energy may be thermal energy or ultraviolet light energy.
The stretching may be bidirectional relaxed, bidirectional unrelaxed, unidirectional relaxed, unidirectional unrelaxed, or parabolic. The subjecting step and the extending step may be performed concurrently.
The method may include adding at least one dichroic dye to the polymeric sheet. The adding step and the subjecting step may be performed concurrently. The adding step may be performed before the subjecting step. The at least one dichroic dye may be a yellow dye, a blue dye, or a combination thereof. The boration treatment may include placing the polymeric sheet in contact with an aqueous solution comprising boric acid. The boric acid concentration may range from about 5% to about 20%. The aqueous solution may include borax. The borax concentration may range from about 1% to about 7%. The polymeric sheet may be supported on a carrier web or a support layer.
In general, in another aspect, the invention features a light polarizer having a molecularly oriented sheet of polyvinylalcohol/polyvinylene block copolymer material having polyvinylene blocks formed by molecular dehydration of a sheet of polyvinylalcohol wherein the molecularly oriented sheet includes light-polarizing molecules of polyvinylalcohol/polyvinylene block copolymer material varying in length, n, of conjugated repeating vinylene unit of the polyvinylene block. An absorption concentration of each of the polyvinylene blocks in the range of n=19 to 25 is not less than approximately 65% of the absorption concentration of any of the polyvinylene blocks in the range of n=14 or 15, wherein the absorption concentration is determined by absorption of wavelengths from about 200 nm to about 700 nm by the polyvinylene blocks. The molecularly oriented sheet exhibits a photopic dichroic ratio, RD, of at least approximately 65.
Implementations of the invention may also include one or more of the following features. The polarizer may include a dichroic dye. The dichroic dye may be a yellow dye, a blue dye, or a combination thereof. A portion of the molecularly oriented sheet may include a moisture-resistance imparting complex of the polyvinyl alcohol/polyvinylene block copolymer and boric acid. A portion of the molecularly oriented sheet may include a moisture-resistance imparting complex of the polyvinyl alcohol/polyvinylene block copolymer and a borax.
In general, in another aspect, the invention features a light polarizer having a molecularly oriented sheet of polyvinylalcohol/polyvinylene block copolymer material having polyvinylene blocks formed by molecular dehydration of a sheet of polyvinylalcohol wherein the molecularly oriented sheet includes light-polarizing molecules of polyvinylalcohol/polyvinylene block copolymer material varying in length, n, of conjugated repeating vinylene unit of the polyvinylene block. An absorption concentration of the polyvinylene blocks at n=25 is not less than approximately 65% of the absorption concentration of any of the polyvinylene blocks in the range of n=14 or 15 wherein the absorption concentration is determined by absorption of wavelengths from about 200 nm to about 700 nm by the polyvinylene blocks. The molecularly oriented sheet exhibits a photopic dichroic ratio, RD, of at least approximately 65.
Implementations of the invention may also include one or more of the following features. The polarizer may include a dichroic dye. The dichroic dye may be a yellow dye, a blue dye, or a combination thereof. A portion of the molecularly oriented sheet further may include a moisture-resistance imparting complex of the polyvinyl alcohol/polyvinylene block copolymer and boric acid. A portion of the molecularly oriented sheet further may include a moisture-resistance imparting complex of the polyvinyl alcohol/polyvinylene block copolymer and a borax.
In general, in another aspect, the invention features a light polarizer having a first polymeric sheet having a first transmission direction and a second polymeric sheet having a second transmission direction. The first polymeric sheet and the second polymeric sheet are molecularly oriented sheets of polyvinylalcohol/polyvinylene block copolymer material having the polyvinylene blocks thereof formed by molecular dehydration of a sheet of polyvinylalcohol. The first transmission direction is oriented 90 degrees from the second transmission direction. The ratio of absorption at 550 nm to absorption at 700 nm is less than approximately 3.75.
Implementations of the invention may also include one or more of the following features. The polarizer may include a dichroic dye. The dichroic dye may be a yellow dye, a blue dye, or a combination thereof. The molecularly oriented sheet may include light-polarizing molecules of polyvinylalcohol/polyvinylene block copolymer material varying in length, n, of conjugated repeating vinylene unit of the polyvinylene block, wherein an absorption concentration of each of the polyvinylene blocks in the range of n=19 to 25 is not less than approximately 65% of the absorption concentration of any of the polyvinylene blocks in the range of n=14 or 15, wherein the absorption concentration is determined by absorption of wavelengths from about 200 nm to about 700 nm by the polyvinylene blocks, and wherein the molecularly oriented sheet exhibits a photopic dichroic ratio, RD, of at least approximately 65. The molecularly oriented sheet may include light-polarizing molecules of polyvinylalcohol/polyvinylene block copolymer material varying in length, n, of conjugated repeating vinylene unit of the polyvinylene block, wherein an absorption concentration of the polyvinylene blocks at n=25 is not less than approximately 65% of the absorption concentration of any of the polyvinylene blocks in the range of n=14 or 15, wherein the absorption concentration is determined by absorption of wavelengths from about 200 nm to about 700 nm by the polyvinylene blocks, and wherein the molecularly oriented sheet exhibits a photopic dichroic ratio, RD, of at least approximately 65.
An advantage of the present invention is it provides an improved K-type polarizer with a higher efficiency and improvement in color.
Another advantage of the present invention is it provides an improved process for producing K-type polarizers.
An additional advantage of the present invention is it provides an improved crossed polarizer with a significant reduction in the leakage in both the blue spectral and red spectral regions.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description, drawings and examples, and from the claims.